[tex]i^{7}=i * (i^{2} )^{3} =i * (-1)^{3}=i * -1 = -i\\i^{9}=i^{7} * i^{2} = -i * -1=i\\i^{10}=i^{9} * i=i * i= i^{2}=-1\\i^{24}=i^{10} * i^{10} * i^{2} * i^{2}= -1 * -1 *-1 * -1=1\\i^{36}=i^{24} * i^{10} * i^{2} =1 * -1 * -1 =1\\i^{21}=i^{10} * i^{10} * i = -1 * -1 * i = i[/tex]
